Polyethylene terephthalate (“2GT”) and polybutylene terephthalate (“4GT”), generally referred to as “polyalkylene terephthalates”, are common commercial polyesters. Polyalkylene terephthalates have excellent physical and chemical properties, in particular, chemical, heat and light stability, high melting points and high strength. As a result they have been widely used for resins, films and fibers.
Polytrimethylene terephthalate (“3GT”) has achieved growing commercial interest as a fiber because of the recent developments in lower cost routes to 1,3-propanediol (PDO), one of the polymer backbone components. 3GT has long been desirable in fiber form for its disperse dyeability at atmospheric pressure, low bending modulus, elastic recovery and resilience.
Feeder yarns (also referred to as “feed yarns” herein, such as partially oriented yarn, “POY”) are typically prepared by melt-spinning of the starting polymer. Feeder yarns do not have the properties required to make textile products without further drawing or draw-texturing, and therefore, are often subject to storage. During storage, prior to subsequent processing, the feeder yarns often age, resulting in loss of properties. As a feed yarn for draw-texturing or drawing, POY is frequently transported from the fiber producer to mills where the POY is drawn-textured or drawn.
A significant aging problem for 3GT POY yarns generally occurs during the time after the yarn is produced from a spinning machine and before the yarn is processed on a drawing or texturing machine. (In contrast, 2GT yarns do not typically age very rapidly during yarn storage time and thus may remain suitable for downstream drawing or draw-texturing operations after storage times as long as, for example, 3 months.) Aging problems in 3GT yarns are especially evident at elevated temperatures during storage and transportation. For example, temperatures of 38° C. and higher may be experienced by yarns during storage in the summer months in a facility without air-conditioning. POY 3GT yarns stored at temperatures of 38° C. or more may become unsuitable for subsequent processing in less than 24 hours.
EP 1 172 467 A1 discloses a process to manufacture 3GT yarn wherein the spinning process and storage are performed under strict conditions of temperature and humidity, 10–25° C. at a relative humidity of 75–90%. This process is impractical for manufacturers who lack air-conditioned storage facilities in warm climates or who ship the spun yarn via truck or other transportation means that lack air conditioning. EP 1 172 467 A1 further discloses that there is a significant impact of temperature on yarn shrinkage, which results in deformed packages that are unsuitable for subsequent drawing and texturing processes.
Similarly, EP 1 209 262 also discloses a 3GT yarn, which was alleged to be capable of being stored and subsequently textured. The patent alleges that the yarn has improved package winding if the fiber has an orientation as determined by birefringence of 0.030–0.070 and a crystallinity as determined by fiber density of 1.320–1.340 g/cm3. A process is provided to produce such fibers by heat treating (50–170° C.) and crystallizing the fibers during a spinning process and immediately winding at “extremely low tension” (0.02–0.20 cN/dtex). However, the disclosed technology in the patent involves the first godet being cold, the second godet being hot, and the package being immediately wound after the hot godet.
JP02129427 reviews the spin-annealing technology that winds the package immediately after the hot godet. According to JP02129427, direct package winding after a hot godet gives a soft threadline caused by high temperature in the threadline between the heated godet and winder. The soft threadline causes a shaking threadline, resulting in increased spinning break or an increased number of misses in package switchover in auto-doff. In addition, in order to improve the yarn uniformity, reduce spinning break, or reduce missing package switchover in auto-doff caused by soft threadline in the technology, the winding tension between the hot godet and winder has to be increased. This increased winding tension made it impossible to avoid tight package winding. Therefore, the technology of winding a package immediately after a hot godet is not the advanced one, which can manufacture PTT-POY without tight package winding, without spinning break or without missing package switchover.
Both U.S. Pat. No. 6,399,194 and JP 01214372 disclose processes in which 3GT yarns undergo a heat treatment step after quench and application of finish to spun fibers prior to being wound. In these processes, hot yarns are directly wound onto packages to avoid the threadline from passing other godet under low tension before winding.
WO 01/85590 discloses heat treating a non-crystalline yarn during spinning. Because the yarn is amorphous, drawing is applied to allow the threadline to pass the second (cold) godet.
JP02129427 recognizes several of the problems encountered in the earlier patents, and places a cold godet after the hot godet prior to winding.
While it is recognized that aging of 3GT feeder yarns is an issue, it would be desirable to provide a spinning process with few spinning breaks that is capable of producing a yarn in a large package size, such as about 6 kg or above, with high uniformity and with low bulge or dish formation. Furthermore, such a process would be desirable which provides a yarn package having stable package formation and stable yarn properties, that is, where the package does not deform and the yarn properties do not change at high storage temperatures, such as 38° C. or higher.